Environmental conditions in subsea wells, such as hydrocarbon extraction wells, are monitored by pressure and/or temperature sensor arrangements located ‘downhole’ at the base of the well bore. Such sensor arrangements are manufactured by at least ten separate manufacturers and each requires an electronic card, supplied by the manufacturer, to interface between the electrical output of the sensor arrangement and the Intelligent Well Interface Standardisation (IWIS) standard adopted by the well operator. Such interface cards are typically located within a subsea electronic module (SEM) normally housed within a subsea control module (SCM) mounted on the well Christmas tree. As an alternative, some SEM suppliers house the cards in a separate container, along with the need for additional connectors. Either method requires a tailor-made configuration of an SEM or separate container for a particular installation, dependent on the well operator's preferences for sensor arrangement type and manufacturer, thus resulting in lack of standardisation and addition and costs to supply SEMs. Furthermore, the delivery timescales of manufacturers' cards invariably do not match the delivery requirements of the well system. This invention substantially reduces the need for tailoring SEMs to cater for different sensor arrangements and thus facilitates SEM standardisation, resulting in cost and delivery delay reduction.